The present invention relates generally to a method and an apparatus for measuring the aridity, temperature, flow rate, total pressure, still pressure, and kinetic pressure of steam at a downhole location within a well through which wet steam is flowing.
In the exploration and production of crude oil, it is often found that the crude oil is too viscous to be recovered, so in many cases, saturated steam has to be injected into the petroleum wells to dilute and force the thick oil out of the downhole wells, thus these wells are called steam injection wells. It is estimated that as much as two thirds of the oil in existing reservoirs cannot be recovered, due to difficulties in measuring downhole environmental conditions. However, the cost of generating and maintaining the steam to recovering the crude oil deposits accounts for a high percentage of the total cost of well operation, and the equivalent of as much as one-third of the total crude oil recovered is required to produce the steam that is required for the recovery process. Therefore, any technique that allows the operator to utilize the steam more efficiently will be useful.
On the other hand, geothermal energy has been used directly for the generation of electricity. Hot water, at a temperature from 140xc2x0 C. to more than 300xc2x0 C. is brought from an underground reservoir to the surface through production wells. Sensing, communication and process control have become commonplace functions during geothermal well drillings.
The measurement of multiple parameters, i.e. aridity, temperature, fluid-flow, still pressure, total pressure, and kinetic pressure of steam, allows the determination of factors affecting the production yield of oil recovery, the consumption of energy, and information concerning the oil reservoirs. Very precise measurements of physical parameters during geothermal well drillings are also highly required in many applications. However, instruments to be used for these measurements and processes must be able to survive in such harsh environments, at high temperature of 400xc2x0 C. and high pressures of 20 MPa or more.
Currently available electrical cables and optical fiber cables cannot directly withstand such high temperatures because their cabling and jacketing materials would be melted immediately. Additionally, the wall of an instrumentation apparatus housing must be sufficiently thick to withstand the high pressure in downhole wells. The combined effects of high temperature and pressure make the fabrication of the sensing apparatus even more difficult, because they may cause high stress on the materials, which may result in inaccurate measurements.
Previously, no apparatus or method has yet been successfully developed for the measurement of even one parameter, except fluid-flow, in steam injection wells, even though great efforts have been attempted. Several approaches have been proposed for the measurement of steam pressure and temperature. One example is that of temperature measurement with a thermocouple, and the use of a hydraulic pressure gauge or other sensor to determine the pressure. Because the boiling points of most working media are below 350xc2x0 C., and the temperature of saturated steam is 400xc2x0 C., this approach has significant difficulties. Another example is the xe2x80x9cspinnerxe2x80x9d flowmeter. However, the spinner flowmeter has a minimum flow velocity sensitivity of about 2 to 4 feet/minute in wells of 4-inch or larger diameter and is not capable of measuring slow fluid flows.
The present invention is a milestone development in apparatus and methods for performing quantitative measurements of the physical properties of steam in harsh environments. Combined with the measurement of two-phase flow properties, it offers a new method and apparatus to directly measure and record aridity, temperature, fluid-flow rate, total pressure, still pressure, and kinetic pressure of steam simultaneously in steam injection wells and in geothermal well drillings. Field tests have demonstrated very promising and exciting results with the high accuracy and reliability that has been impossible in the past.
Accordingly, it is an object of the present invention to provide a method and an apparatus that are capable of measuring the aridity, temperature, fluid-flow rate, total pressure, kinetic pressure, and still pressure of steam in a high-temperature and high-pressure environment with accuracy and reliability.
It is another object of the present invention to provide a method and an apparatus that are capable of measuring the aridity, temperature, fluid-flow rate, total pressure, kinetic pressure, and still pressure of steam at high-temperature and high-pressure within a downhole well, such as a steam injection well or a geothermal production well, with accuracy and reliability.
It is a further object of the present invention to provide a method and an apparatus that are capable of measuring the aridity, temperature, fluid-flow rate, total pressure, kinetic pressure and still pressure of steam flowing inside a steam pipe with accuracy and reliability.
Objects of the present invention are achieved by providing a sensing apparatus that includes a combination of several fiber optic sensors having metal shell-housings and heat insulation means that protect said fiber optic sensors on an interconnected electronic circuit board, and allow their survival and proper operation the harsh high-temperature and high-pressure environments.
The apparatus of the present invention provides many advantages. First, the apparatus directly measures and stores the data necessary to determine multiple engineering parameters associated with the steam in a well. Second, many multi-parameter measurements may be obtained each time the apparatus is inserted into and withdrawn from the well, allowing comparison between measured data to insure valid data, and to obtain information concerning the variation in the properties of the steam at different height positions in the well. Additionally, said steam properties at different locations within the well and different temperatures, pressures, aridities and flow rates may be obtained and combined to determine the state and the state changes of the single phase or multi-phase well steam. Moreover, a specially designed shell and heat insulation mechanism keep the temperature inside the apparatus below 80xc2x0 C., which allows the multiple-parameter measurements to be made with high accuracy and reliability, so the apparatus can be used for a very long time.